Perhaps the question is no longer whether to have a main feature, but what kind of choices you could give. What are the options beyond what you have ready…following hashtags, follows of my follows…
Discussion
That's where I'm at. As long as any kind of curation is simply an optional choice fully in the control of the user, I'm cool with it.
Nostrgram could be a kind of content curation service. Empowering people with different options.
By your comments and even the settings options you make available now, it looks like you’ve got the spirit for offering choice.
I like the “speak your mind” in your note text box. Perhaps you could free up some head room by making that static at the bottom of the page and using 100% width, or adding a large floating button on a bottom corner that would then expand the box for note making.
That may allow you to focus on possible tabs…and to make content discovery the main focus.